1. Field of the Invention
This invention relates to a lithographic printing method, an ink supplying apparatus for use in the lithographic printing method and a printing press equipped with the ink supplying apparatus.
2. Description of the Related Art
In emulsion-ink based lithographic printing, emulsion ink that attaches itself to a form roller to be supplied to a lithographic printing plate mounted on a plate cylinder in contact with the form roller has the emulsion (specifically, the droplets of its aqueous component) disrupted so that printing is performed with the aqueous component of the emulsion ink having been separated to serve as fountain solution. Compared with the conventional lithographic printing method that separately supplies ink and fountain solution, the emulsion-ink based lithographic printing has the advantage of simplifying the ink supplying apparatus by eliminating the device for supplying fountain solution, with the resulting cost reduction, greater ease in operating the ink supplying apparatus and the like.
Further mention needs to be made of the conventional lithographic printing method which employs separately supplied ink and fountain solution. If printing is to be performed under conditions that are prone to cause scumming as exemplified by the use of a lithographic printing plate having a propensity for scumming, only fountain solution may be supplied to the surface of the lithographic printing plate on the plate cylinder in idling mode which is defined as such a condition that the form roller is out of contact with the plate cylinder before start of printing (i.e. before feeding), and when printing is thereafter started or just before start of printing, the form roller is brought into contact with the surface of the printing plate and the ink is supplied, thereby ensuring that printed matter without scumming is obtained right after starting the printing operation. If printing is to be performed under such conditions that ink receptivity is low as exemplified by the use of a lithographic printing plate of low ink receptivity, only ink may be supplied to the surface of the lithographic printing plate on the plate cylinder in idling mode, and when printing is thereafter started or just before start of printing, fountain solution is supplied, thereby ensuring that printed matter of high ink receptivity is obtained right after starting the printing operation.
However, in the emulsion ink-based lithographic printing method which, as mentioned above, has the aqueous component of the emulsion ink separated as it is on the form roller in contact with the plate cylinder, it is impossible to ensure that either fountain solution or ink is selectively supplied to the surface of the lithographic printing plate on the plate cylinder.
Therefore, when emulsion ink-based lithographic printing is performed by the use of a lithographic printing plate having a propensity for scumming or the like, the ink adhering to the non-image areas is not easy to clean up, causing problems such as the need to prolong the idling mode before start of printing and the development of massive waste paper due to scumming right after starting the printing operation. When it is performed by the use of a lithographic printing plate having low ink receptivity or the like, the ink does not easily attach itself to the image areas, causing problems such as the need to prolong the idling mode and the development of massive waste paper due to poor ink build-up right after starting the printing operation.
Further, the printing press adapted to emulsion inks of the contemplated type, as compared to those which employ conventional non-emulsion inks, has fewer rollers in contact with the printing plate on the plate cylinder, so that the ink will not easily attach itself to the image areas of the printing plate, thereby not only extending the time of idling mode before printing starts but also increasing the chance for the development of massive waste paper.
An object of the present invention is to provide an emulsion ink-based lithographic printing method by which the duration of idling mode can be shortened while reducing the development of waste paper right after the start of the printing operation even if the printing is performed by the use of a lithographic printing plate prone to cause scumming, one that has low ink receptivity or the like, and to provide an apparatus suitable for use in the method.
The present invention provides the following lithographic printing methods (1)-(3), ink supplying apparatus (4) and printing press (5).
(1) A lithographic printing method of performing lithographic printing by supplying emulsion ink to a lithographic printing plate via a form roller, comprising the steps of:
supplying the emulsion ink to the form roller; and
disrupting emulsion on the form roller, with a degree of the emulsion""s disruption being changed before and after a start of printing.
(2) The method according to (1), wherein the degree of the emulsion""s disruption is changed such that the degree after the start of printing is smaller than that before the start of printing.
(3) The method according to (1), wherein the degree of the emulsion""s disruption is changed such that the degree after the start of printing is greater than that before the start of printing.
(4) An ink supplying apparatus for supplying emulsion ink to a lithographic printing plate via a form roller, comprising the form roller from which emulsion ink is supplied, an emulsion disruptor for disrupting emulsion in the emulsion ink on the form roller, and an emulsion disruption controller by which a degree of disruption of the emulsion by the emulsion disruptor is changed before and after a start of printing.
(5) A printing press comprising the ink supplying apparatus according to (4).
As described below, if the present invention is applied to emulsion ink-based lithographic printing, the duration of idling mode can be shortened with the added advantage of reducing the development of waste paper right after the start of printing.